Reciprocating piston engines typically comprise a plurality of variable volume combustion chambers, each chamber being defined by a reciprocating piston in a cylinder bore. The pistons are coupled to a crankshaft which is driven by movement of the piston caused by gas expansion in the chamber. These engines operate by compressing an air/fuel mixture in the working cylinder prior to igniting the mixture or by injecting fuel into hot compressed air to initiate combustion. The crankshaft assembly converts the work generated by the combustion process into torque available at the end of the crankshaft.
The moment of ignition in the cylinders is controlled depending on number of factors such as engine speed and air/fuel ratio. Since an engine typically includes a plurality of cylinders, the combustion process not only has to be controlled in a single cylinder but in all of the cylinders. If the combustion process is improperly controlled, engine knock may occur which releases very large amounts of heat within a short space of time which may cause damage to the piston, cylinder head and cylinder head gasket.
Control of the combustion process is a particular problem in engines which are to be operated in a homogenous charge compression ignition (HCCI) mode, also known as Activated Radical (AR) combustion or Active Thermo-Atmosphere Combustion (ATAC). The HCCI mode is an auto ignition mode which differs from the phenomenon of engine knock in that the reaction rate between the fuel and air is slowed down by diluting the fuel with air and/or exhaust gas so as to produce a combustion which is sufficiently slow so as not to ruin the engine. While HCCI is fuel efficient, it is difficult to control as a large time delay is required between the start of fuel injection and the start of fuel combustion.
It is known to monitor the combustion process using in-cylinder pressure sensors. From the analysis of the combustion pressure inside the cylinder, it is possible to determine the start and the speed of the combustion process. This information can be used to control the combustion process of the next cycle by controlling the fuel injection timing and/or opening and closing of the intake and outlet valves for example.
It is known to position a sensor within each cylinder which has the advantage of providing a detailed and highly accurate measurement of the combustion process which can be used to control the ignition timing. However, the provision of an in cylinder sensor in each of cylinders is expensive and, depending on the engine layout, may not be possible.
It is also known, for example from DE 102 33 612 A1, to control the combustion phasing of a plurality of cylinders by using one or more vibration sensors positioned adjacent the cylinders, for example on the engine head. However, although this arrangement has the advantage of reduced cost, the information which can be gained from this indirect measurement is relatively inaccurate and the improvement in control which can be achieved is limited.
It is, therefore, desirable to provide a system and a method of controlling combustion phasing in an internal combustion engine which overcomes at least some of these problems. In addition, other desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.